There are several different types of Tuition Assistance. As a National Guard officer, you will be eligible to receive Federal and State Tuition Assistance the day you commission. You will also become eligible for the Montgomery G. I. Bill upon the completion of Officer Basic Leadership Course- Reserve Component (OBLC-RC).
If you have yet to apply for medical school. It may be beneficial for you to check out the tuition assistance offered by the various states. Some states offer full tiution reimubrsement for graduate schools including medical school. Yes that's right, you could be earning 45K per year and pay nothing for your school.
While I hope to write more about these benefits in the future, you can find much of what you need in the sub-page links directly, below.